Centrifugal machine with differential drive



Dec. 3l, 1968 MAsuxcHl YAsuDA r-:TAL 3,419,211

CENTRIFUGAL MACHINE WITH DIFFERENTIAL DRIVE Filed Oct. 23, 1967 $.A RDA www .T NAGmA EYOIW ru V K '.MA NIOIN IHV'K KAWVW U SMOH AKmO W MAHT United States Patent O 3,419,211 CENTRIFUGAL MACHINE WITH DIFFERENTIAL DRIVE Masuichi Yasuda, Toyonaka, Akira Yokogawa, Osaka,

Hiroyuki Ito, Fuse, and Toshio Niwa, Osaka, Japan, assignors to Hitachi Shipbuilding and Engineering C0. Ltd., Osaka, Japan Filed Get. 23, 1967, Ser. No. 677,320 9 Claims. (Cl. 233-7) ABSTRACT F THE DISCLSURE The difference in rotational velocity between the basket or bowl and the screw of the inventive centrifugal machine is provided by a combination of a drive cylinder acting as a power input for the bowl, a circular spline secured to the cylinder, and a flexible, elliptical spline disposed inside of and in partial mesh with the circular spline, the former being connected to the screw shaft. The drive mechanism replaces the conventional intricate planetary gearing, the source of repeated disturbances.

The invention relates to a centrifugal machine of the Screw type and, more particularly, to a machine having a new differential drive adapted to rotate *both the basket or bowl and the screw of the centrifugal machine, at predetermined different velocities.

Centrifugal machines of the screw type are adapted continuously to subject a slurry to centrifugal forces so as to separate the solids from the liquid portion or phase of the slurry, and may generally be of two types: one having a filter basket and another which is equipped with a sedimentation bowl.

In the case of a machine with a filter basket, the liquid is discharged through a plurality of openings in the filter screen. In the case of a centrifugal machine having a sedimentation bowl, the liquid is allowed to overliow the bowl, and the solids remaining in the bowl are discharged by means of a screw, the revolution of which is slightly different from that of the bowl.

To attain a sufficiently high centrifugal force, which would naturally vary with different slurries, it is essential to provide for a number of revolutions that produces a centrifugal force of the order of hundreds to thousands times gravity. For this purpose, the basket or bowl must of necessity be driven at extremely high velocities.

In order to provide for some difference in the rotational speeds between the shafts of the bowl and the screw, it has been conventional to employ a complicated mechanism involving planetary gears or similar expedients. However, such a :mechanism has been found to pose serious problems in the design and engineering of centrifugal machines, in addition to the noise of operation that ensues from the use of such a mechanism. A frequent breakdown of the machine is usually the result.

The object of this invention is to provide a centrifugal machine having a new drive system, which is light in weight and sturdy in construction.

It is another object of the invention to make use 0f previous developments in so-called strain-wave gearings, improving their principle and adapting the same to the particular requirements of centrifugal machines.

According to one of the main features of the invention, the centrifugal machine comprises, in combination, a basket or bowl as well as a screw adapted to discharge the solid phase of the slurry that is centrifuged; a driven cylinder for rotating the bowl; a circular spline secured to the cylinder a-nd having internal teeth; and a flexible, elliptical spline fitted inside the circular spline and having external teeth which are partly in mesh with the teeth of the circular spline. The shaft of the elliptical spline is connected to the drive shaft of the screw, thereby producing a difference in rotational velocity between the bowl and the screw.

According to other important features, the screw is rotated at a velocity only slightly higher than that of the bowl. Thus, for example, the screw shaft may be imparted 2000 r.p.m. while the bowl shaft is driven at 1990 r.p.m. by the differential drive of the centrifugal Inachine. Other combinations are o-f course possible. For the above-mentioned speed ratio, the respective splines will have 199 and 200 teeth, respectively.

Yet another inventive feature relates to the provision of a roller `bearing disposed on the peripheral surface of an elliptical cam inside the elliptical spline for rotatably supporting the latter.

The invention provides separate outlets lfor the liquid phase and the remaining, squeezed cake or solid phase of the centrifuged slurry. In a preferred, exemplary embodiment these outlets are provided at opposite ends of the bowl and screw structure.

Still another inventive feature relates to means for maintaining the long axis of the elliptical spline, and its cam, normally in a vertical position. A torque arm is provided, rigid with the elliptical cam and articulated, or otherwise movably connected, to a -xing lever which, in turn, is subjected to the action of an appropriate brake mechanism.

Thus, the system including the circular and the elliptical splines is normally held in said vertical position. Any deviation from an equilibrium condition between the reaction force, generated as a result of the discharge of the solid phase, and the force transmitted from the braking mechanism, will temporarily swing the long axis out of the vertical position. This feature avoids jerks and makes lfor smooth running of the centrifugal machine even under heavy load conditions.

The various objects, features and attendant advantages of the present invention will become more apparent from the following description of a preferred, exemplary embodiment, when considered in conjunction with the accompanying drawing wherein:

FIG. l is a side-elevational view, partly in section. of a horizontal centrifugal m-achine embodying the principles of this invention; and

FIG. 2 is a somewhat diagrammatic sectional view, taken along line II-JII in FIG. l, showing the construction of the drive system used according to this invention.

The invention will hereinafter be described in full detail. In the exemplary, horizontal centrifugal machine illustrated in FIG. 1, the slurry to be centrifuged is charged into a hollow cylindrical chamber 2 through a charging or inlet pipe 4. A centrifuge screw 6, alsn termed conveyer screw, is secured to the periphery of the chamber 2. The separated liquid phase is discharged through an outlet tube 8 while the squeezed cake or solid phase is `discharged through another outlet tube. numbered 10.

A drive shaft 12 is directly connected to a basket or bowl 14 adapted to accelerate the slurry to be centrifuged, and the shaft 12 is supported by a bearing 16 attached, in turn, to the framework of the centrifuge (to which reference will be had later). The shaft 12 is driven by an electric motor or the like prime mover, shown at 1S, by way of V-belts 20 acting on a drive cylinder 22 which is secured, by keys 24, to the end of the drive shaft 12. The motor 18 is preferably fitted with a conventional pulley 26 around which the V-belts 20 are guided. It will be understood, however, that other conventional power transmission means may be used to the same effect in the inventive centrifugal machine.

The frame of the machine is generally designated 28 while a separate supporting structure 30 may be provided, as shown, for the bearing 16.

The differential drive mechanism of the centrifugal machine includes a circular spline 32 having internal teeth 34, the spline being disposed inside the drive cylinder 22. Thus, the spline 32 is driven together with the above-mentioned bowl or basket 14.

Inside of the circular spline 32l is disposed a flexible spline 36 preferably made of durable elastomeric material and having external teeth 38 thereon. As will hereinafter be described in further detail, this spline 36 is constantly adjusted to an elliptical configuration by an elliptical cam 40 in a plane normal to its shaft.

A torque arm 42 is provided which keeps the cam 40 stationary by aid of a shaft 44 against the drive cylinder 22. The lower end of the arm 42 has a sliding fit with a fixing lever 46 secured to a shaft 48 directly connected to H a suitable braking mechanism 50.

It will be understood that the flexible spline 36 is in engagement with the circular spline 32, by way of its external teeth 38, only at the ends of the long axis of the cam 40, while the remaining teeth 34 and 38 remain unengaged (see FIG. 2).

A cylindrical element 52 is secured at its base to the shaft 54 of the screw 6 by suitable, conventional means, and reaches to the spline 36, for delivering power.

The elliptical cam 40 is preferably provided with bearing rollers S6, as shown, and serves, in fact, as the inner race of the latter, while the fiexible spline 36 functions as the outer race thereof, As illustrated, the elliptical cam 38 is fixed, by means of the shaft 44, so that the long axis of the cam 40 is vertical at all times.

The teeth 34 and 38 of the circular and elliptical splines 32, 36, respectively, have the same circular pitch but the pitch circle of the elliptical spline 36 is smaller than that of the circular spline 32 by a distance equal to the tooth differential. Thus, as the basket or bowl 14 turns, the circular spline 32 is also driven therewith. The elliptical spline 36 also tends to be driven likewise, but, as has hereinbefore been explained, the number of teeth of the elliptical spline 36 is smaller than that of the circular spline 32, and consequently the former turns at a velocity higher than that of the latter, by the velocity equivalent to the tooth differential.

Thus, the conveyor or screw shaft 54 which is connected to the fiexible or elliptical spline 36, by way of the cylindrical element 52, is driven at a velocity somewhat different from that of the bowl 14, with the result that the solids are driven out of the bowl by the force corresponding to the very difference in velocity. Such a difference in rotational speeds, unless it is very small, cannot result in an effective discharge of the solids from the bowl.

In accordance with the present invention, since the number of teeth of both splines 32, 36 may be virtually made as large as desired, it is possible to obtain an infinitesimaily small difference in velocity at very large numbers of revolutions. Examples of this relation are given below:

Number of teeth of- Circular spline 32 400 200 }etc Elliptical spline 36 398 199 as a result of the discharge movement of the squeezed cake or solid phase from the basket or bowl 14, is transmitted to the torque arm through the screw shaft S4, the cylindrical element 52, the fiexible or elliptical spline 36, the ball bearing 56, the elliptical cam 40 and the shaft 44.

In other words, when the reaction force is in equilibrium with the braking force transmitted through the fixing lever 46, the elliptical cam 40 is kept vertical, as shown in FIG. 2

Consequently, the rotational velocity of the bowl 14, which is connected to the drive cylinder 22 through the hollow drive shaft 12, is smaller than that of the screw 6 which is secured to the cylindrical element 52 through the shaft 54. Then, the very difference of the rotational velocities between the bowl and the screw produces the separating and discharging force against the squeezed cake.

It may be added that a modified version of the differential drive mechanism described and illustrated herein may be used advantageously in continuous-type centrifugal machines, such as a preferred embodiment disclosed in a copending, co-assigned patent application entitled Continuous-Type Centrifugal Machine, Ser. No. 677,321, filed Oct. 23, 1967.

Some of the structural elements of the present application are correlated hereunder, for the sake of better understanding, with the corresponding elements of the copending application, as follows: the screw and the bowl of this application, with their respective shafts, identified by numerals 6, 14, 54 and 12, correspond to elements 6, 2, 8 and 4, respectively, of the other application; the driving motor 18 and the drive cylinder 22 have their counterparts in the motor 12 and V-pulley 10 of the other case; the slurry inlets are 4 in this case and 36 in the other, while the liquid outlets are numbered 8 and 60a, and the solid outlets 10 and 54, respectively, in the two applications.

The foregoing disclosure relates only to a preferred, exemplary embodiment of the invention, which is intended to include all changes and modifications, as well as additions to the example described, which are within the scope and spirit of the invention as set forth in the objects and features outlined in the preamble, and the appended claims.

Thus, it will be appreciated, the inventive features disclosed in this application may be embodied in a vertical machine as well although it has been shown herein, as a matter of illustration, for a horizontal centrifugal machine.

What we claim is:

1. A centrifugal machine with differential drive, comprising, in combination, bowl means capable of rotating at a velocity suficiently high to separate a slurry into liquid and solid phases; screw means capable of rotating at a velocity slightly higher than that of said bowl means; said bowl means and said screw means having respective drive shafts; and a mechanism for separately driving said bowl means and said screw means at predetermined different velocities, said drive shafts being substantially coaxially supported in conjunction with said mechanism; the latter including a drive cylinder secured to the drive shaft of said bowl means, and having -means for receiving power from a prime mover, a circular spline rigidly secured within said drive cylinder and having internal teeth, a flexible, elliptical spline rotatable inside said circular spline and having external teeth, some of which are in engagement with some of said internal teeth, and a stationary elliptical cam within said elliptical spline, the latter being secured tothe drive shaft of said screw means; whereby said bowl means and said screw means are driven at the predetermined different velocities to effectively discharge the solid phase from said bowl means.

2. The centrifugal machine as defined in claim 1, further comprising a roller bearing disposed on the peripheral surface of said elliptical cam for rotatably supporting said elliptical spline.

3. The centrifugal machine as defined in claim 1, wherein said splines have both a considerably large num ber of teeth, with only a slight ditierence therebetween.

4. The centrifugal machine as defined in claim 3, wherein the ratio of the numbers of teeth between said circular and said elliptical splines is 2001199.

5. The centrifugal machine as dened in claim 1, wherein the respective teeth of said splines make a planar contact, resulting in a high torque carrying capacity.

6. The centrifugal machine as defined in claim 1, wherein said splines lhave different pitch diameters.

7. The centrifugal machine as defined in claim 6, wherein said teeth of the splines have the same diametral pitch.

8. The centrifugal machine as defined in claim 1, wherein some of said teeth of the respective splines are in engagement substantially at both ends -of the long axis of said elliptical cam, and further comprising means for maintaining the long axis in a predetermined position, in equilibrium between the reaction force, generated by the discharge of said solid phase, and a counter force pr-ovided by said maintaining means.

9. The centrifugal machine as defined in claim 8, wherein said maintaining means includes a torque arm rigid at one end with said elliptical cam, a fixing lever movably connected to the other end of said torque arm, and means for applying the counter force against displacement of said fixing lever, thereby restoring any temporary deviation of the long axis from the predetermined position due to transient overload conditions.

References Cited UNITED STATES PATENTS 2,867,378 l/1959 Harlow 233-7 3,187,997 6/1965 Gooch 233--7 3,228,593 1/1966 Topping 233-7 ROBERT W. JENKINS, Primary Examiner. 

